There are a thousand and one reasons why this can happen, however, here two examples to think about.

1. The interview may not have gone as well as you thought it did particularly in cases where the interviewer already decides that you are not the right fit for the role. The interviewer might come to this decision because he or she considers you to be a poor communicator. You can be perceived as a poor communicator due to several reasons that include but are not limited to: speaking with a very heavy accent, speaking in a dis-jointed way (a lack of structure to your conversations), speaking too fast or too slow (the concept of pacing needs to be applied consistently) and so on. 
2. Change in hiring plans: this can happen at any time in the process and usually, interviewers are not able to predict such occurrences ahead of time. Companies that estimate their hiring budget accurately and well in advance should of course have this at the barest minimum. This change might involve some internal restructuring which might lead to the role being scrapped.

I won’t claim to be a communication expert however there are some basic things you can do to improve yourself. Please find below a list of them.

1. Identify the actual challenge. Are you a fast talker? Are you used to starting another sentence before completing the previous one? You need to identify the actual issue by asking the interviewer or recruiter who gave you this feedback. In cases where that doesn’t work, go ahead and ask friends and acquaintances for their feedback. If possible seek the opinion of people that do not share the same nationality or mother tongue with you. The reason is that these people might not be able to help you identify what the major issue is.
2.  Consider learning and practising how to pace when speaking. Employ this intentionally in the everyday conversations you have so that you can make a habit out of it. Pacing in simple terms would require you to speak at the speed of the person you are speaking with.
3. When asked a question, ensure you understand the question before you go ahead to answer the question. One way to ensure that you are on the same page with your interviewer is to rephrase his or her question and to ask them if that is what they are asking you to answer. In cases where you don’t fully understand the question asked, don’t be afraid or shy to ask clarifying questions to help you understand the question they are asking.
4. Solicit feedback from your interviewer as you speak e.g at intervals pause and ask questions like; I hope that is in line with what you asked? I hope I am not speaking too fast for you? I hope that explanation is clear enough? e.t.c

The primary suspect is generally your resume. It is important to pay attention to how adapted your resume is to the job description. In general, nobody wants to receive the resume of a medical doctor for a role that asks for a lawyer. The responsibility of adapting your resume lies solely with you because the person reviewing your cv might not be interested in making direct correlations on your behalf. In a nutshell, ensure that your resume is dummy-proof and that it tells a clear and consistent story so that the person reading your resume can directly correlate all of the information presented there to the requirements of the role that you have applied to. It is also important to do away with internal job titles; so for example, if the role of the Tech lead is internally called a chief whip, what should be on your resume should be tech lead and not chief whip because that is the title that is recognized by the job market. Using market recognisable names would make your resume more understandable.

I personally believe that there is no right or wrong answer to this particularly if you are applying to jobs in Germany where putting your picture on your resume seems to be the in-thing. My answer would be to do what feels comfortable for you. However, if you decide to put your picture on your cv, take care to put a picture that portrays the environment you are applying to. In other words, applying to a start-up company with a fully suited and ‘all too serious’ looking picture might portray you as just that. In general start-up companies are not that formal. However, applying to a corporate or an environment that favours formal dressing might require you to put your suited and ‘all too serious’ looking picture. I generally advise you to add a smile to your face irrespective of what form of attire you decide to go with. The smile has a way of making you look friendly and relatable.

Try to self reflect, there might be something you can feature on your resume. For example, were you part of any association in school? Did you hold any leadership position? Are you leading or part of a group of people in any religious organisation? and what does this entail? and the likes. Do you have skills that you have built by virtue of any of this, and can you apply these skills in the role you are applying to?. Also, you might want to consider serving as a volunteer to gain some experience. Finally reaching out to your network and leveraging Linkedin might also yield better results.